在Python中,格式化字符串时,我可以按名称而不是按位置填充占位符,如下所示:

print "There's an incorrect value '%(value)s' in column # %(column)d" % \
  { 'value': x, 'column': y }

我想知道这在Java中是否可能(希望没有外部库)?


当前回答

不完全是,但你可以使用MessageFormat多次引用一个值:

MessageFormat.format("There's an incorrect value \"{0}\" in column # {1}", x, y);

上面的事情也可以用string .format()来完成,但是如果你需要构建复杂的表达式,我发现messageFormat语法更干净,而且你不需要关心你放入字符串中的对象的类型

其他回答

这是一个旧的线程,但只是为了记录,你也可以使用Java 8风格,像这样:

public static String replaceParams(Map<String, String> hashMap, String template) {
    return hashMap.entrySet().stream().reduce(template, (s, e) -> s.replace("%(" + e.getKey() + ")", e.getValue()),
            (s, s2) -> s);
}

用法:

public static void main(String[] args) {
    final HashMap<String, String> hashMap = new HashMap<String, String>() {
        {
            put("foo", "foo1");
            put("bar", "bar1");
            put("car", "BMW");
            put("truck", "MAN");
        }
    };
    String res = replaceParams(hashMap, "This is '%(foo)' and '%(foo)', but also '%(bar)' '%(bar)' indeed.");
    System.out.println(res);
    System.out.println(replaceParams(hashMap, "This is '%(car)' and '%(foo)', but also '%(bar)' '%(bar)' indeed."));
    System.out.println(replaceParams(hashMap, "This is '%(car)' and '%(truck)', but also '%(foo)' '%(bar)' + '%(truck)' indeed."));
}

输出将是:

This is 'foo1' and 'foo1', but also 'bar1' 'bar1' indeed.
This is 'BMW' and 'foo1', but also 'bar1' 'bar1' indeed.
This is 'BMW' and 'MAN', but also 'foo1' 'bar1' + 'MAN' indeed.

在编写本文时,Java中还没有内置任何东西。我建议编写自己的实现。我的偏好是一个简单流畅的构建器接口,而不是创建一个映射并将其传递给函数——你最终会得到一个漂亮的连续代码块,例如:

String result = new TemplatedStringBuilder("My name is {{name}} and I from {{town}}")
   .replace("name", "John Doe")
   .replace("town", "Sydney")
   .finish();

下面是一个简单的实现:

class TemplatedStringBuilder {

    private final static String TEMPLATE_START_TOKEN = "{{";
    private final static String TEMPLATE_CLOSE_TOKEN = "}}";

    private final String template;
    private final Map<String, String> parameters = new HashMap<>();

    public TemplatedStringBuilder(String template) {
        if (template == null) throw new NullPointerException();
        this.template = template;
    }

    public TemplatedStringBuilder replace(String key, String value){
        parameters.put(key, value);
        return this;
    }

    public String finish(){

        StringBuilder result = new StringBuilder();

        int startIndex = 0;

        while (startIndex < template.length()){

            int openIndex  = template.indexOf(TEMPLATE_START_TOKEN, startIndex);

            if (openIndex < 0){
                result.append(template.substring(startIndex));
                break;
            }

            int closeIndex = template.indexOf(TEMPLATE_CLOSE_TOKEN, openIndex);

            if(closeIndex < 0){
                result.append(template.substring(startIndex));
                break;
            }

            String key = template.substring(openIndex + TEMPLATE_START_TOKEN.length(), closeIndex);

            if (!parameters.containsKey(key)) throw new RuntimeException("missing value for key: " + key);

            result.append(template.substring(startIndex, openIndex));
            result.append(parameters.get(key));

            startIndex = closeIndex + TEMPLATE_CLOSE_TOKEN.length();
        }

        return result.toString();
    }
}

你可以在字符串助手类上有这样的东西

/**
 * An interpreter for strings with named placeholders.
 *
 * For example given the string "hello %(myName)" and the map <code>
 *      <p>Map<String, Object> map = new HashMap<String, Object>();</p>
 *      <p>map.put("myName", "world");</p>
 * </code>
 *
 * the call {@code format("hello %(myName)", map)} returns "hello world"
 *
 * It replaces every occurrence of a named placeholder with its given value
 * in the map. If there is a named place holder which is not found in the
 * map then the string will retain that placeholder. Likewise, if there is
 * an entry in the map that does not have its respective placeholder, it is
 * ignored.
 *
 * @param str
 *            string to format
 * @param values
 *            to replace
 * @return formatted string
 */
public static String format(String str, Map<String, Object> values) {

    StringBuilder builder = new StringBuilder(str);

    for (Entry<String, Object> entry : values.entrySet()) {

        int start;
        String pattern = "%(" + entry.getKey() + ")";
        String value = entry.getValue().toString();

        // Replace every occurence of %(key) with value
        while ((start = builder.indexOf(pattern)) != -1) {
            builder.replace(start, start + pattern.length(), value);
        }
    }

    return builder.toString();
}

谢谢你的帮助!使用所有的线索,我写了一个例程来做我想要的——使用字典的类似python的字符串格式化。因为我是Java新手,任何提示都是感激的。

public static String dictFormat(String format, Hashtable<String, Object> values) {
    StringBuilder convFormat = new StringBuilder(format);
    Enumeration<String> keys = values.keys();
    ArrayList valueList = new ArrayList();
    int currentPos = 1;
    while (keys.hasMoreElements()) {
        String key = keys.nextElement(),
        formatKey = "%(" + key + ")",
        formatPos = "%" + Integer.toString(currentPos) + "$";
        int index = -1;
        while ((index = convFormat.indexOf(formatKey, index)) != -1) {
            convFormat.replace(index, index + formatKey.length(), formatPos);
            index += formatPos.length();
        }
        valueList.add(values.get(key));
        ++currentPos;
    }
    return String.format(convFormat.toString(), valueList.toArray());
}

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